Description

frozen_string_literal: true

The Version class processes string versions into comparable values. A
version string should normally be a series of numbers separated by periods.
Each part (digits separated by periods) is considered its own number, and
these are used for sorting. So for instance, 3.10 sorts higher than 3.2
because ten is greater than two.

If any part contains letters (currently only a-z are supported) then that
version is considered prerelease. Versions with a prerelease part in the
Nth part sort less than versions with N-1 parts. Prerelease parts are
sorted alphabetically using the normal Ruby string sorting rules. If a
prerelease part contains both letters and numbers, it will be broken into
multiple parts to provide expected sort behavior (1.0.a10 becomes 1.0.a.10,
and is greater than 1.0.a9).

Prereleases sort between real releases (newest to oldest):

1.0

1.0.b1

1.0.a.2

0.9

If you want to specify a version restriction that includes both prereleases
and regular releases of the 1.x series this is the best way:

Users expect to be able to specify a version constraint that gives them
some reasonable expectation that new versions of a library will work with
their software if the version constraint is true, and not work with their
software if the version constraint is false. In other words, the perfect
system will accept all compatible versions of the library and reject all
incompatible versions.

Libraries change in 3 ways (well, more than 3, but stay focused here!).

The change may be an implementation detail only and have no effect on the
client software.

The change may add new features, but do so in a way that client software
written to an earlier version is still compatible.

The change may change the public interface of the library in such a way
that old software is no longer compatible.

Some examples are appropriate at this point. Suppose I have a Stack class
that supports a push and a pop method.

Versions shall be represented by three non-negative integers, separated by
periods (e.g. 3.1.4). The first integers is the “major” version number,
the second integer is the “minor” version number, and the third integer is
the “build” number.

A category 2 change (backwards compatible) will increment the minor version
number and reset the build number.

A category 3 change (incompatible) will increment the major build number
and reset the minor and build numbers.

Any “public” release of a gem should have a different version. Normally
that means incrementing the build number. This means a developer can
generate builds all day long, but as soon as they make a public release,
the version must be updated.

Let’s work through a project lifecycle using our Stack example from above.

Version 0.0.1

The initial Stack class is release.

Version 0.0.2

Switched to a linked=list implementation because it is cooler.

Version 0.1.0

Added a depth method.

Version 1.0.0

Added top and made pop return nil
(pop used to return the old top item).

Version 1.1.0

push now returns the value pushed (it used it return nil).

Version 1.1.1

Fixed a bug in the linked list implementation.

Version 1.1.2

Fixed a bug introduced in the last fix.

Client A needs a stack with basic push/pop capability. They write to the
original interface (no top), so their version constraint looks
like:

gem'stack', '>= 0.0'

Essentially, any version is OK with Client A. An incompatible change to
the library will cause them grief, but they are willing to take the chance
(we call Client A optimistic).

Client B is just like Client A except for two things: (1) They use the
depth method and (2) they are worried about future
incompatibilities, so they write their version constraint like this:

gem'stack', '~> 0.1'

The depth method was introduced in version 0.1.0, so that
version or anything later is fine, as long as the version stays below
version 1.0 where incompatibilities are introduced. We call Client B
pessimistic because they are worried about incompatible future changes (it
is OK to be pessimistic!).

Let’s say you’re depending on the fnord gem version 2.y.z. If you specify
your dependency as “>= 2.0.0” then, you’re good, right? What happens if
fnord 3.0 comes out and it isn’t backwards compatible with 2.y.z? Your
stuff will break as a result of using “>=”. The better route is to
specify your dependency with an “approximate” version specifier (“~>”).
They’re a tad confusing, so here is how the dependency specifiers work: